1. Field of the Invention
The disclosure relates to an iontophoresis device for administering dissociated drug ions through an ion-exchange membrane that selects ions of the same polarity as that of the drug ions, capable of further enhancing the administration efficiency of the drug ions.
2. Description of the Related Art
An iontophoresis device generally includes a working electrode structure holding drug ions dissociated to positive or negative ions and a nonworking electrode structure that functions as a counterpart of the working electrode structure. The drug ions are administered to a living body by the application of a voltage with the same polarity as that of the drug ions to the working electrode structure under the condition that both the structures are in contact with a biological interface such as the skin or mucous membrane of the living body (e.g., human being or animal).
In this case, the charge supplied to the working electrode structure is consumed by the movement of the drug ions to the living body and the release of biological counter ions (the ions which are present in the living body and charged in a polarity type opposite to that of the drug ions), and the biological counter ions (e.g., Na+ and Cl−) having a small molecular weight and hence having a high mobility are released mainly from the living body. Thus, the ratio of the charge consumed by the release of biological counter ions increases, which makes it impossible to administer drug ions effectively.
JP 3040517 B, JP 2000-229128 A, JP 2000-229129 A, JP 2000-237326 A, JP 2000-237327 A, JP 2000-237328 A, JP 2000-237329 A, JP 2000-288097 A, JP 2000-288098 A, and WO 03/037425, the disclosures of which are incorporated herein by reference, disclose iontophoresis devices that have solved the above-mentioned problem.
More specifically, in each of the iontophoresis devices above, a working electrode structure is composed of an electrode, a drug holding part placed on a front side (in contact with the skin) of the electrode, and an ion-exchange membrane that is placed on a front side of the drug holding part and selectively passes ions with the same polarity as that of the drug ions held by the drug holding part, and the drug ions are administered through the ion-exchange membrane, whereby the release of biological counter ions is suppressed to enhance the administration efficiency of the drug.
In each of the iontophoresis devices above, the working electrode structure further includes an electrolyte solution holding part for holding an electrolyte solution in contact with the electrode, and an ion-exchange membrane that selectively passes ions having a polarity that is opposite to that of drug ions, thereby achieving the additional effects of preventing the drug ions from being decomposed by isolating the drug ions from the electrode and preventing the movement of H+ or OH− ions generated at the electrode to the drug holding part and the biological interface of a living body.
Here, in the iontophoresis devices of JP 3040517 B, JP 2000-229128 A, JP 2000-229129 A, JP 2000-237326 A, JP 2000-237327 A, JP 2000-237328 A, JP 2000-237329 A, JP 2000-288097 A, JP 2000-288098 A, and WO 03/037425, in order to facilitate the passage of drug ions with a relatively large molecular weight and effectively suppressing the release of biological counter ions from a living body, an ion-exchange membrane is used in which a semi-permeable film made of polyolefin, vinyl chloride-based resin, fluorine-based resin, or the like is filled with ion-exchange resin (resin provided with an ion-exchange function). As such a semi-permeable film has low affinity for the biological interface of a living body, it is difficult to keep the contact between the ion-exchange membrane and the biological interface of the living body in a satisfactory state during the administration of drug ions, and depending upon the site which a working electrode structure and a nonworking electrode structure are brought into contact with, the behavior of the living body (patient) during the administration, and the like, the administration efficiency of drug ions cannot be maintained at a desired or sufficient level.
Therefore, the following inconvenience is caused. During the administration of the drug ions, it is necessary to interpose an electrolyte solution or the like between the ion-exchange membrane and the biological interface of the living body, or further keep pressing the working electrode structure and the nonworking electrode structure against the biological interface of the living body with some bias means.
The same kind of problem also arises in other devices that conduct the passage of a current to a living body, such as a low-frequency therapeutic equipment. In these devices, an adhesive film in which acrylic hydrogel is impregnated with an electrolyte solution is used, whereby the adhesion between the electrodes and the living body, and the conductivity are ensured.
However, when an adhesive film containing an electrolyte is interposed between the ion-exchange membrane and the skin, the function of the ion-exchange membrane in suppressing the release of biological counter ions from the biological interface degrades. Consequently, in the iontophoresis device for administering drug ions through an ion-exchange membrane, the administration efficiency of a drug cannot be enhanced by the use of this type of adhesive film.